Spin physics by the SMC

The Spin Muon Collaboration at CERN has covered a wide range of spin physics. The main aim of the collaboration was the measurement of the $g_{1}$ spin structure functions of the proton and the neutron (using deuteron targets) in the range $0.003<x<0.7$ for $Q^{2} \geq $ 1 GeV$^{2}$. This was accompanied by a QCD analysis of all published $g_{1}$ data. The spin structure functions $g_{2}$ were also measured, which allowed for a reduction on the error in $g_{1}$. Semi-inclusive data were analyzed in order to produce the first polarized quark distributions. Data obtained with a dedicated low $x$ trigger extend down to $x=6 \times 10^{-5}$ for $Q^{2} \geq$ 0.01 GeV$^{2}$. Some more specifics channels are still being analyzed, they include asymmetry in diffractive $\rho$ production, hadron azimuthal asymmetry with a transversely polarized target, measurement of the longitudinal $\Lambda$ polarization, and the asymmetry in high $P_{t}$ hadron pair production. This last asymmetry is related to the gluon polarization in the nucleon, and this topic is discussed in some details after a brief review of the main inclusive results.